Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.1902m&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #19.02; Bulletin of the American Astronomical Society, Vol. 24, p.1150
Astronomy and Astrophysics
Astronomy
Scientific paper
The chemically peculiar magnetic He-Strong star sigma Orionis E is also one of the most luminous nonthermal stellar radio sources in the sky at centimeter wavelengths. Previous radio Very Long Baseline Interferometry (VLBI) measurements have established that the emission comes from a region of very high brightness temperature (Tb =~ 10(10) K) no larger than 6R_⋆ in extent. Andre (1987, 1990) has modeled the radio emission as originating from a stable, dipolar magnetosphere. Since sigma Ori E is an oblique rotator whose magnetic and rotational axes differ by ~ 70deg , any flattened morphology for such a magnetosphere would lead to viewing-angle effects as the star and magnetosphere corotated. A series of intercontinental VLBI measurements were therefore carried out to look for a changing projected radio size versus rotational phase, which would be expected if a flattened, corotating magnetosphere is responsible for the nonthermal radio emission. No correlation was noted with projected radio size and rotational phase. In the same measurements, a correlation between circular radio polarization and rotational phase was evident. The correlation appears to be in the sense that magnetic pole-on aspects show circular polarization, changing helicity sense as each magnetic pole moves through our field of view. During equator-on phases, the circular polarization vanishes. These radio polarization and structural results will be discussed in the context of previously claimed correlations of total radio intensity as a function of rotational phase for this star (Leone et al 1992). In particular, the postulated thermal jets of Leone et al can be ruled out as a model for explaining the circularly polarized, high brightness temperature radiation from sigma Ori E. A peristellar, magnetic nonthermal model is supported by the VLBI and polarization results.
André Ph.
Miller Kenneth A.
Phillips Robert B.
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